The ethics of removing invasive plants

Nature Talk
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The other week, someone left a comment next to one of my observations, noting that the plant was invasive and I should remove it when I find it. I knew that that plant was invasive, and have actually removed it other places, but have never thought of doing so in parks. I got to thinking about the reason I don’t try to remove invasive plants. These are a few of them:

  1. It could be counter-productive. Obviously it is often trying to drain the ocean with a spoon, but it could go beyond that. Since invasive plants often do better on disturbed ground, pulling them out of the soil and leaving more ground bare might just give more ground for their seeds to land on.

  2. It could create erosion or other environmental hazards. Along with creating conditions for more seed dispersal, tearing plants out of the ground can lead to erosion conditions, as well as (in some places) creating more tinder for fires. It also can be just plain ugly.

  3. I am pretty confident in my identifications, but… not 100% sure. I guess part of me is afraid that while I might think I am ripping up some common English Ivy, it could be some rare, endemic species. Not much of a chance, but “first, do no harm”

How do you feel about removing invasive plants?

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My local county and state parks (in california), as well as most local open spaces prohibit removing any plants unless part of an officially supervised volunteer work group. However, I have visited preserves where the docents encouraged us To remove noxious weeds from wildflower trails. I would agree with your cautious approach - do no harm.

(However, I often hike with a friend who knocks the immature seed heads off of noxious weeks)

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If I have the time and the will, I pull garlic mustard and the yankable honeysuckles. It really depends on where I’m at though. If I see one patch of garlic mustard in an otherwise very well-managed wood, you bet I’m going to pull them up. Not worth my time if they are outnumber me severely.

As for your worry about freeing space for more invasives, I can only say that I am trying to turn the garden space around the perimeter of my house into a native plant only zone, and so far just removing the invasives and non-natives as they appear has worked really well! It helps that it’s my property and I can keep up with it regularly, but the natives moved in surprisingly quickly once I removed the competition.

I wish city/county/state parks were managed for invasive plants more carefully. Or at all. The best managed land in my area are Bur Oak Land Trust properties (not government owned), as they periodically get volunteers together to remove invasives. You can really tell the difference.

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I try to remove invasive plants whenever possible in my own back woods, but I usually refrain from doing so on public woods unless it’s the odd garlic mustard. I was with a team at Burnet Woods a three years ago removing invasive plants en masse, but in most cases I think it’s better to let the professionals deal with it if you’re alone.

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I think the idea that soil disturbance should be an impediment to invasive species removal is overblown. It is less bad than the presence of the invasive species on a basic level, but the question does bring up a crucial, often overlooked point: weed removal is only successful with thorough followup. Even devoted habitat restoration outfits sometimes struggle with this. A goal and a strategy ought to be defined for any invasive species work. Basically, don’t take on a weed removal project if you’re not willing to go back next year and the next and the next. Consider revegetation with local, appropriate native species. A deeper commitment like this eliminates the worry about whether the weed will flush after this generation is pulled.

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I take out young Chinese Privets - Ligustrum sinense in the local park(s) when ever I can. Best time for uprooting is fresh after at least a couple days’ rain.

I’ve had a small amount of success taking out very small Beefsteak plant - Perilla frutescens populations in an area with a battery operated weed-eater. This was back before I knew what they were. I let them flower to get the ID, then wacked them all down. I’ve had no seeds germinate in this area since. Don’t know how they got there in the first place, but they cease to exist now. (Do not use a weed-eater if they’ve already flowered, you’ll just spread seeds then.) Best time to do this is at the end of the growing season just as the flowers begin opening.

I’ve significantly lowered the number of Japanese honeysuckle - Lonicera japonica on the properties of my relatives by simply following the vines back to the main root mass. Once you uproot where it all began, the rest of the plant soon follows.

Kudzu - Pueraria montana My only advice is to take out the very young plants before they’re impossible to uproot. But even destroying small plants has proven to be a difficult task. Their roots grow very deep very fast, so be prepared to use some muscle.

Get your IDs checked, then show no mercy. Have fun picking!

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I have spent the last few years intensively managing invasive plants using mechanical means in my woods and meadows. I have experimented (and continue to do so) with many techniques and I have to agree with others regarding soil disturbance, as I’ve never seen a significant increase in invasive plants simply due to my removal of another species. In one instance, I pulled all the barberry plants out of a three-acre infestation, and was worried I would get nothing but garlic mustard as it was already prevalent, but instead I got only white snakeroot, wood asters and bluestem goldenrod and had hardly any increase in the garlic mustard. Please keep in mind that the tiny amount of soil that is disturbed in pulling a barberry shrub is nothing compared to the amount of soil disturbance that is entirely normal for these same forests; tip-up mounds create a lot more exposed soil than pulling invasive plants.

I won’t go too much into the techniques I use as I am still experimenting with them, but think it is very important not to wipe out an invasive plant population entirely unless there is already well-established native vegetation, as you are more likely to degrade the habitat that way (I once accidently ruined yellow warbler nesting habitat on my land years ago by removing all the multiflora rose and buckthorn from one area). I generally like to work with the native vegetation, using it as a tool to kill invasive species (such as cutting the multiflora rose root sprouts instead of mowing them so that the native willows, dogwoods and alders may take their place and outcompete them). I definitely advise against any significant herbicide use or mowing.

Most importantly, remember that every plant is unique in its biology and ecology and two species will respond to the same control method in different ways. For example, I find I can effectively manage multiflora rose simply by cutting it, but barberry must be pulled. Don’t just think that every plant can be managed the same as every other plant.

Also, many of the invasive plants I am dealing with are the direct result of various historical disturbances, and that replicating these disturbances will not help the situation. Many of which thrive in overgrazed pastures, poorly managed roadsides, deer overbrowsed forests, etc… Truly healthy ecosystems in my region largely resist significant invasion by invasive plants.

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Clidemia hirta is a problem in Hawaii, and most places are too far gone for single-person scale removal to do any good. But as I was hiking up Mt. Ka`ala, I got above the infested zone, and there, I did pull out each Clidemia seedling I found. But then, higher still, I came to an established bush that I could not pull, and it demoralized me.

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This is in the family of problems that suffer from both a tragedy of the commons (problem is too big for any individual) and from an expertise hurdle (it’s hard to know what the right approach is). I’m finding them all over these days, and have a sense of ever-increasing urgency. It’s upsetting.

I recommend doing what you can, educating yourself and others, but being humble and forgiving of people with good intentions who do different.

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I know that with some plants, pulling them out can actually just let them spread through the area even more. I’ve recently encountered a problem with some japanese knotweed managing to get into the garden, and it seems that removing it without the proper procedures just leads it to send up new stems even more quickly

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Ditto.
There’s also the fact that park officials (or other public land stewards) may wish to do removal themselves to document it for their own invasive tracking initiatives*.

*[addendum: things I might not have had time to record, or might not even think to record: eg., those spots on the leaves in my Melia azedarach observation - are they feeding scars? If so, is what’s feeding on this invasive the kind of information TPWD wants to record? Number and distance of adult trees of the same species? etc.]

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1, 2 and 3 are all spot-on! Weeding in Reserves is my life-long hobby, but for all the reasons you gave, it should not be done without expert knowledge (I’m self-taught but always seeking out experts, books, the experience of others etc) and the best assessment one can make of the ecology there and the role the weed/s are playing in the current situation.

The most valuable lesson I ever had was 23 years ago from a native plant specialist nurseryman visiting a roadside “wasteland” I had been working on. In a weed-covered culvert were several native ferns that I had released from invasive grasses. I asked him if, exposed as they had become, they would survive the coming summer. He said “this one may, this one probably won’t” etc.

He was absolutely right. So by weeding them I killed them.

Ever since I have been trying to improve my ability to assess likely rate of growth of both weed and native, and find the ideal rate and technique of weed-removal to avoid loss of shade and ground cover, while creating and maintaining enough space for the optimum development of the native.

Exactly the same principles apply to trees. Cutting down invasive trees can result in the loss of trees around them…not to mention the loss of fruit that has been feeding birds.

But because I always felt, like you, that interfering with the plants was rightly forbidden, ( though in fact there appear to be no rules about it here) I was extremely thoughtful and cautious from the start, so I was able to learn a lot from a little change, and build up from there.
[EDIT I should have added that I am still not sure when and how much weeding to do, and still occasionally leave what I am pretty sure is a weed, especially seedlings, until I can be 100% sure, eg when its older. And with the current drought here everything has to be rethought entirely.

I was talking with a person recently about the concept of casual volunteers, ie one-day groups, removing weeds in forest reserves and the other person said, “its not rocket science”. I thought a moment, then said, “Actually it IS rocket science”, as it feels like that to me. I am always reviewing the results of what I have done and am increasingly aware of how little I know.

I wish everyone thought like you. We lose a lot of native plants around here from well-intentioned attempts.

So I think you should get some training and get stuck in:)

In Auckland, NZ here we are the Weed Capital of the World, they say. And there is virtually no budget for doing anything about it, so the little work that is contracted is done at the gallop and with chemicals, which is obviously not ideal.

Being a volunteer means I can go off-trail into the fragile forest legitimately, treading lightly and carefully of course. So for me weeding in “my” bit of park is a joy and a privilege I couldn’t live without.

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I’ve removed Himalayan balsam both as part of an organised group and on my own. That’s relatively easy to do and unlikely to cause any harm (at least where I live in the south of England). There are a couple of small patches which now have native plants but were 90% Himalayan balsam before I cleared it. We’re hoping to clear it from a local stream & woodland over the next few years. It may be possible to eliminate there as it’s a self contained area.

That’s something wouldn’t touch unless it was on my land and I’d done lots of research. I think professionals use methods which aren’t available to the public (in the UK at least) like injecting herbicide. I think it is possible to control without herbicide but tricky. In the UK you can be held responsible if you fail to control it and it spreads.

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I don’t have any real opinion on this question, but do have a couple of things to add. I’ve lived long enough to see the introduction of several invasive species, and the attempts to either eliminate them or control their spread. None have been successful. As an example, it should have been possible to keep zebra mussels confined in Eastern Canada, but they are now common in Manitoba even though we are part of a different watershed. The general public moves around too much, and doesn’t practice good hygiene (like washing boats, not transporting wood). Eventually, the organisms just become another part of the ecosystem. So unless there is a well organized program to eliminate a life form when it gets a toe hold in a place, I think it’s a lost cause. Unless the removal of invasive plants will do damage, digging them up will likely make people feel better, but won’t have much of a long term impact.

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Coming from the Point of view of a person who does Invasive Species removal in Protected Areas for a living… (I deal primarily with Phragmites, Garlic Mustard and Spotted Knapweed and am a licensed pesticide applicator where its warranted, pulling and cutting is used in most cases.)

We don’t encourage the general public to undertake this work without proper permissions and supervision for many reasons that you’ve identified.

First its illegal to harm/kill plants or animals other/organisms found within many reserves. I’ve encountered many well meaning people who have harmed/ripped out native plants. (Often Mistaking Cow Parsnip for Giant Hogweed.) I do know some sites where erosion is a concern and disturbance has caused the problem in the first place. We prefer people to notify staff personally or through citizen science like INat, EDDMaps where the organisms are and how plentiful they are. So that the site can be checked, confirmed and the best and safest method for removal can be brought to bare. As well as ensuring site rehabilitation with native species or at least mulch to assist in the suppression of the seed bank. We know and appreciate this is sometimes a slow process.

As its often the case that expertise, people power and resources may be lacking, approaching protected area managers with best practices guidelines from reputable agencies and offers of assistance may go a long way in developing partnerships and getting the job done. Keep in mind that we have approval policies, environmental assessments, Volunteer agreements and liability to deal with so if the process is slow and wrapped in red tape don’t take it personally. We want to deal with infestations while they are small and manageable but the big picture is managers have a great deal of other concerns on their plates beyond the pulling of weeds. (Especially in times of Covid where the public shows up in unsustainable numbers, the washrooms are blowing up with non flushable wipes and the trash piles up faster than it can be removed) Unfortunately this often means invasives are lower priorities.

It is a tricky line to walk for certain.

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Yikes. You can hurt yourself messing with this plant.

I second the guidance given here about working with land managers when on public land. It’ll be safer, legal, and probably more effective. Cutting and/or mechanical removal will only get you so far. Chemical treatment is often needed or introducing prescribed fire. And one final note, registered volunteer workers really help agencies justify budgets and demonstrate efficient use of funds. Nothing says you love your public natural places more than going through all the trouble to become a volunteer.

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Among our Cape Town fynbos, I do pull smallish invasive weeds when I see them (especially Australian wattles)

Thanks to iNat I learned a new invasive yesterday
https://www.inaturalist.org/observations/10921201

And again thanks to an iNat project - these 4 sturdy trees were removed after I reported them
https://www.inaturalist.org/observations/34454270
https://www.inaturalist.org/projects/alien-early-detection-rapid-response-s-afr

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I think that the decision on the eradication of an alien species could be made weighting pros and cons in terms of ecological services and disservices. Of course for me not all the services and disservices should have the same weight, being the risk for replacement of rare native species the most important.
If it is sure that an alien cannot spread any further and the risks related to its presence are low, it could be taken in consideration to keep it there. As an example, in a green area in the middle of Livorno I suggested to keep a bush of Broussonetia papyrifera. I does not set fruit and can be shown to citizens as an example of invasive plant.
On the other hand I suggested to remove a population of the invasive Bidens frondosa that had completely covered a wetland almost not allowing any other species to colonyze that area.

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Speaking of ecological services provided by invasives and other nonnatives,
https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1366-9516.2001.00120.x

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Also, to be clear, when I talk about reasons not to remove invasive plants, I mean when they are found in public places.

If I am working in my own yard, or in a place I am very familiar with, I am going to try to remove invasive plants. But I am probably not going to do so while just out casually hiking.

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